Where stand alone or independent electrical batteries are desired to power an electrical subsystem in an aircraft, battery life is of course a problem. And an electrical battery source independent from the existing electrical system of the aircraft may be desired, especially where retrofitting of the aircraft is done.
In general, it is well known that when the aircraft is on the ground it doesn't normally require any power.
The foregoing is illustrated by U.S. Pat. No. 4,581,571 granted to James E. Hansen entitled "Electrical Power Disconnect System." And that patent discloses a system that opens the main battery switch of the aircraft when the plane is on the ground. Normally the pilot would open such main battery switch. But if this is not done, the Hansen patent provides that conditions such as weight being on the wheels of the plane will automatically open the battery switch to thereby void "unnecessary depletion of the battery." The Hansen system, however, does not deal with a stand alone subsystem on the aircraft but the main battery; moreover, it is sensitive to a ground condition and not to a "flight" condition.